Honeydew Honey

"Honeydew" is a classification of honey that refers to honey produced by honeybees collecting nectar that is exuded from another insect such as an aphid or scale insect. It is quite common in a number of countries and the best known is honeydew from the Black Forest in Germany. World wide honeydew can be referred to variously as "forest honey", "Pine honey", "Fir honey" etc. and may sometimes be referred to by the specific species of tree producing the honeydew.

Typically honeydews have lower levels of glucose and fructose and higher levels of complex sugars due to the extra enzymatic actions in the sap sucking insect's gut. Honeydews don't normally crystallize due to the reduced levels of glucose and also have a high mineral content which is measured as a high conductivity - this measurement being the main tool to differentiate honeydews in the laboratory.

New Zealand Beech Honeydew honey is one of New Zealand's premium export honeys. It has a history of export to Europe and specifically Germany since the early 1970s. There are several honeydew producing scale insects in New Zealand inhabiting a variety of plants. However most of these are small honeydew sources or intermittent production. The beech forests of the South Island are a different story however. Two species of beech tree inhabited by two species of honeydew insect (the sooty beech scales) from the Margarodidae family produce New Zealand's largest single exported honey crop. The beech trees are Black Beech (Nothofagus solandri) and Red Beech (N. fusca). The two insects are Ultracoelostoma assimileand U. brittini. U. brittini tends to inhabit the trunks and larger branches, while U. assimile is recorded (C.F.Morales) as favouring the upper branches and twigs, thus U.brittini is the insect most likely to be encountered by the casual observer wandering in the beech forests.

The black colour of trees and plants with a honeydew source is due to the growth of a black sooty mould (Capnodium fungus) on the surplus nectar exuding over the plant and sometimes even the ground. Particles of this fungus are typically found in honeydew being referred to as "honeydew elements" and are used as a part of the identification as honeydew.

Droplets of nectar are highly visible to any observer visiting the beech forest, but bees are rarely seen collecting these. Mostly they are observed foraging on the bark and particularly at the base of the tubules extending from the scale insect buried under the bark.

Colour

Beech honeydew is one of our darker honey types with a Pfund Scale average of 87.6mm and a Standard Deviation (SD) of 12.9mm (1,125 records). Colour does depend to some extent on area. There are some areas that do produce darker honeydew. Whether this is due to local conditions or blends of lighter (non honeydew) honeys is uncertain but we can find no correlation between conductivity and colour. Honeydew is generally a slower honey flow than most of the other flower honeys (although there are exceptions of course), and honeybees prefer to store honeys like this closer to the brood nest, typically in darker combs. This can darken the colour of the resultant honey.

New Zealand Beech honeydew is typical of most honeydews in having a high conductivity. This arises from the nature of honeydew production. An insect of the Hemiptera order of insects (those with sap sucking mouthparts e.g. aphids, scale insects etc.) sucks sap from the host plant and exudes a sweet sticky nectar which is essentially slightly modified sap. This is then collected by honeybees as a nectar source and is "ripened" into honey. This pathway is quite different from that of normal flower honeys. The direct sucking of the sap, the additional insect in the production chain with many additional enzymatic processes taking place, and the presence of sooty moulds, all add up to an additional mineral content not normally found in flower honeys. This is indirectly measured by the ability of honeydew to conduct electricity. The average conductivity for Beech honeydew is 1.19 mS/cm SD .22 mS/cm ( 1,390 records) which is around 10 times the average for flower honeys. This high level of mineral and trace elements is thought to be of significant nutritional value, one of the key reasons honeydew is popular in Europe.

Carbohydrate ProfileHoneydews in general are normally low in glucose and they are also lower in fructose than flower honeys. This low glucose and fructose is supplemented by higher levels of more complex sugars such as maltose, erlose and melezitose. This has the effect of reducing the tendency to crystallize. Beech honeydew is likewise very slow crystallizing and in fact some beech honeydews never crystallize. Typical values for Beech Honeydew are: Glucose 22.9% - SD 2.0% (400 samples), Fructose 33.8% - SD 2.1% (400 samples). Sucrose 0.67% - SD 0.81% (400 samples) SD = Standard Deviation.

OligosaccharidesAnother feature of New Zealand beech honeydew is the presence of oligosaccharides (complex sugars) in greater levels than average flower honeys.

It has been shown that oligosaccharides are helpful in maintaining and promoting beneficial bacteria in the gut (probiotic bacteria), particularly after treatment with antibiotics. As such oligosaccharides are classed as "prebiotics" i.e. a food for probiotics.

Antioxidants New Zealand Beech Honeydew is similar to other honeydews in having higher levels of antioxidants than most other flower honeys. In a study at Lincoln University, Beech Honeydew had the highest levels of polyphenolics, one of the most significant classes of antioxidant compounds. Additionally, using the ABTS and ORAC methods for antioxidant calculation, Beech Honeydew consistently ranked near the top of 10 monofloral honey varieties tested. The results of these three tests indicates that New Zealand Beech Honeydew has one of the highest levels of antioxidants of all New Zealand honeys. Other high ranking honeys include Thyme, Manuka and Rewarewa - all dark coloured, strong flavoured honeys.

Antibacterial Activity Honeydew has very high levels of Glucose Oxidase activity giving a high degree of antibacterial activity that often exceeds levels found in manuka honey. We are currently collaborating on further research into Glucose Oxidase activity in Honeydew.

Moisture Content - Presence of Yeast

Normally honeydew is below 17% moisture. In the main production area, fermentation is not generally a concern, but the environment is such that large populations of yeast can occur in the honeydew forests. This is due to the presence of large quantities of a food resource (honeydew nectar) and, particularly after rain, wet conditions. At times the forest can smell quite sour with a fermentation smell and wasps can be observed drunk on the tree trunks. Under these conditions, high levels of yeast may occur in honeydew honey that come from this environment, rather than from fermentation of the ripened honey. It is possible that this may be marked against the product as a perceived quality issue, rather than it being a natural occurrence.

"A series of oligosaccharides based upon successive addition of glucose (1->4) to the glucopyranosyl residue of sucrose and another series similar to the first but with the final residue linked (1->6) have been isolated from New Zealand honeydew honey and fully characterized. Because the trisaccharide in this series is erlose, it is inferred that the honeydew of the indigenous scale insect, Ultracoelostomaassimile, which lives upon the Southern beech, Nothofagus spp,. is of the erlose type. These oligosaccharides and others have been quantifed by GC and LC in six New Zealand honedew honeys"

This paper is available online from the publisher at www.acs.org for US$25.00 in PDF format. The author (to whom correspondence should be addressed) is manleyha@waikato.ac.nz